clean up tail call transformer

lib/6to5/transformation/templates/tail-call-body.js

@@ -4,9 +4,11 @@
       SHOULD_CONTINUE_ID,
       RESULT_ID;
 
+  var CALLEE_ID = FUNCTION;
+
   do {
     SHOULD_CONTINUE_ID = false;
-    RESULT_ID = FUNCTION.apply(THIS_ID, ARGUMENTS_ID);
+    RESULT_ID = CALLEE_ID.apply(THIS_ID, ARGUMENTS_ID);
   } while(SHOULD_CONTINUE_ID);
 
   return RESULT_ID;

lib/6to5/transformation/transformers/es6/tail-call.js

@@ -43,9 +43,11 @@ function transformExpression(node, scope, state) {
           leftId,
           node.left
         );
+
         if (node.operator === "&&") {
           testExpr = t.unaryExpression("!", testExpr);
         }
+
         return [t.ifStatement(testExpr, returnBlock(leftId))].concat(callRight);
 
       case "SequenceExpression":
@@ -122,21 +124,17 @@ var functionChildrenVisitor = {
     if (t.isReturnStatement(node)) {
       // prevent entrance by current visitor
       this.skip();
+
       // transform return argument into statement if
       // it contains tail recursion
       return transformExpression(node.argument, scope, state);
     } else if (t.isFunction(node)) {
-      return this.skip();
+      this.skip();
     } else if (t.isTryStatement(parent)) {
       if (node === parent.block) {
-        return this.skip();
-      } else if (node === parent.finalizer) {
-        return;
-      } else {
-        if (parent.finalizer) {
-          this.skip();
-        }
-        return;
+        this.skip();
+      } else if (parent.finalizer && node !== parent.finalizer) {
+        this.skip();
       }
     }
   }
@@ -201,6 +199,7 @@ exports.FunctionExpression = function (node, parent, scope) {
     SHOULD_CONTINUE_ID: shouldContinueId,
     ARGUMENTS_ID:       argumentsId,
     RESULT_ID:          resultId,
+    CALLEE_ID:          scope.generateUidIdentifier("callee"),
     FUNCTION:           t.functionExpression(null, node.params, block),
     THIS_ID:            thisId,
   });